This program of research seeks to identify the behavioral and psychological functions mediated by the hippocampus and attempts to determine how the hippocampus is functionally integrated with the brainstem, hypothalamus and neocortex in the regulation of behavior. By means of electrical stimulation and reversible cryogenic blockade of brainstem-hypothalamic systems, stimulation of which causes contrasting types of electrical patterns in the hippocampus (theta rhythm or desynchronization), we manipulate the state of hippocampal activity and determine the effect upon spontaneous and trained behaviors and upon the different stages of sleep and wakefulness. The trained behavioral performances against which the effects of electrical stimulation of, or cryogenic blockade of, medial and lateral hypothalamic pathways is evaluated are: visual discrimination tasks in which the role of attention can be minimized or maximized, visual memory measured in delayed response tasks, and operant learning or conditioning in which voluntary motor response and motivational factors can be assessed. Electrophysiological activity in hippocampus and in anterior and posterior neocortical sites are recorded during performance of behavioral tasks. Behavior is monitored by video camera and electrically recorded activity is also monitored by video camera and the two sets of concurrent events are simultaneously displayed on a video monitoring screen and also recorded on video tape for later analysis. A variety of acute experiments have been carried out in order to determine the optimal locations for stimulating and recording electrodes in chronic preparations, and similarly for cryoprobes. Of particular importance are acute and semi-chronic experiments in which the mechanism of pacemaker cells in the septum which drive hippocampal theta rhythm is being studied. The results will contribute to a better understanding of the role of the hippocampus and related brain structures in the control and regulation of brain electrical activity and behavior. The results should also have application to the understanding of mental and behavioral disorders associated with the limbic system.